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Transcript
Chapter 12 FORCES of EVOLUTIONARY CHANGE Evolution & Populations Evolution – a descent changewith in allele modification frequency • Calculation: Descent – implies inheritance • Modification – a change in heritable number of copies of a particular allele traits from toingeneration total numbergeneration of alleles present the population Microevolution Population = a group = relative of interbreeding short-term members genetic changes of the same withinspecies a population or species; the generation to generation Gene pool changes in–allele all the frequencies genes and their alleles within a population Evolutionary Thought Buffon – suggested that closely related species arose from a common ancestor and changed as they spread Lamark – suggested that organisms that used one part of their body repeatedly would increase their abilities, conversely disuse of body parts would weaken an organ until it disappeared; such changes would pass to future generations Charles Darwin: The Voyage of the HMS Beagle In the fourth Ship’s naturalist year,aboard the ship the ship, HMS spent a month Beagle in the on its 5-year voyage around Galápagos Islands the coast of South America In the Galápagos Islands, Recorded Darwin would observations form his theory on the results of evolution of geological by natural forces selection and the fossils he discovered: • Forest plant fossils mixed in sea sediments • Marine fossils found in a mountain cave Charles Darwin: The Influential Ideas Lyell • Principles of Geology – natural processes are slow and steady, and the Earth is much older than 6000 years idea Malthus • Essay on the Principles of Population – individuals better able to obtain resources were more likely to survive; those that could not would die Charles Darwin: Darwin’s Finches Different types of finch found on the Galápagos islands probably descended from a single ancestral type Gradually the finch population branched in several directions, exploiting the various resources each island offered Charles Darwin: Natural Selection Descent with modification Natural selection – environmental factors cause the differential reproductive success of individuals with a particular phenotype (genotype) On the Origin of Species – 1859 The single, most powerful idea in biology Modern Evolutionary Theory The connection between natural selection and genetics: • Genetic mutations create heritable variations • This variation is the raw material upon which natural selection acts • DNA mutations occur at random in all organisms • Sexual reproduction results in genetically different offspring Figure 12.8 Natural Selection What does Adaptations Elimination Natural selection “Survival of add phenotypes to does reproductive ofnot the have Fittest” asuccess goal mean? • Fitness Adaptation Natural selection – an=organism’s any cannot indirectly featurereproductive control that changes provides the a selective allele mutation contribution frequencies ofadvantage genes to theinnext a because population generation it • Fitness improves Individuals Natural selection depends the with organism’s poorly on cannot theadapted ability generate abilitytoto a phenotypes “perfect” survive and just organism reproduce long are “weeded enough to out” reproduce • Natural Individuals Selected selection successful with the can promotes best phenotypes only adaptations work any trait with are are the entirely what that increases is most genetically a matter likely anoforganism’s to available thereproduce time and infitness, a place • even The adaptations (environmental population if that traitconditions is are detrimental passedundergo ontotothe the offspring change organism’s constantly) survival Generation1 Multiple generations later Generation2 Antibiotic present Time Time Staphylococcus aureus before mutation Mutation occurs (red) Reproduction and Selection Antibiotic-resistant bacteria are most successful Hardy-Weinberg Equilibrium Hardy-Weinberg At Hardy-Weinberg equilibrium equilibrium, is aallele highly frequencies unlikely situation and genotype – it occurs frequencies only in do not change from populations that meet generation the following to generation assumptions: • No Allele natural frequency: selection • No mutations number of copies of a particular allele • Infinitely large population total number of alleles present in the population • Random mating •• Genotype frequency: No movement of individuals into or out of the population number of individuals with a particular genotype total number of individuals present in the population Figure 12.12 Hardy-Weinberg Equations Dd Dd The equations Two equations provide represent a framework the relationship for between allele determining whether frequencies evolution and has genotype frequencies: occurred; in reality, allele frequencies change when: • Some Allele frequencies: phenotypes are better adapted (natural selection) • Mutations addp new + q =alleles 1.00 • Chance events occur • Mating Genotype is selective frequencies: Allele Frequencies • Individuals travel between populations p2 + 2pq + q2 = 1.00 Dd Dd DD Genotype Frequencies DD DD dd Dd Dd Dd DD dd Dd dd Female gametes D DD d DD Dd Dd Male Dd gametes Dd DD D Dd p2 = (0.6)2 = 0.36 DD pq = (0.6)(0.4) = 0.24 dd d Dd DD pq = (0.6)(0.4) = 0.24 p2 + 2pq + q2 = 1 p = frequency of D (dominant allele) = dark fur = 0.6 q = frequency of d (recessive allele) = tan fur = 0.4 p+q=1 dd q2 = (0.4)2 DD = 0.16 Figure 12.13 Natural Selection Shapes Populations Stabilizing selection Directional Disruptive selection selection–––two intermediate oneor extreme more extreme phenotypes phenotype is fittest are fittest Light Small Medium Dark Large Medium Light Dark Pigmentation Pigmentation Birth weight Health problems Habitat changes; for extremes Habitat changes; mix of light trees darken and dark rocks of individuals Number of individuals Number Number of individuals Number of individuals Number of individuals Number of individuals Directionalselection Disruptive Stabilizing selection Light SmallLight Medium Dark Medium Large Dark Pigmentation Birth Pigmentation weight Sexual Selection Influences Reproductive Success Sexual selection – a type of natural selection resulting from variation in the ability to attract a mate • Members of the same sex compete among themselves for mates • Members of one sex choose particular members of the opposite sex Sexual dimorphism – a difference in the appearance between males and females of a species Additional Mechanisms of Evolution Mate selection Mutation Chance events: – a change – a preference in an organism’s for a •DNA particular Genetic sequence phenotype; drift –introduces a change typically in a new allele a female allele into selection frequency the population; process due to athe chance only source event of •new Founder allelesevent – occurs when a small Migration group is–isolated members from entering the home and interbreeding population with an existing population • Bottleneck introduce neweffect alleles; – occurs departing when members a take population their alleles decreases with them in number over a relatively short period of time Chapter 13 EVIDENCE of EVOLUTION The Geologic Timescale: 4,600 – 248 MYA Permian 248 First conifers; fewer amphibians, more reptiles; cotylosaurs and pelycosaurs; Pangaea supercontinent forms 290 Paleozoic era Phanerozoic eon Carboniferous Reptiles arise; ferns abundant; amphibians diversify; first winged insects 354 Bony fishes, corals, crinoids; amphibians arise, land plants and arthropods diversify Devonian 417 First vascular plants and terrestrial invertebrates; first fish with jaws Silurian 443 Ordovician Algae, invertebrates, graptolites, jawless fishes; first land plants 490 “Explosion” of sponges, worms, jellyfish, “small shelly fossils”; ancestors of all modern animals appear; trilobites Cambrian Precambrian supereon 543 Eukarotes appear; O2from photosynthesis accumulates in atmosphere Proterozoic eon 2,500 Archean eon Life starts 3,800 Hadean eon 4,600 Earth forms The Geologic Timescale: 248 MYA – Recent Recent Quaternary Human civilization 0.01 Homo sapiens, large mammals; ice ages Pleistocene 1.8 Cenozoic era Australopithecus ,modern whales 5.3 Hominoids; mammals continue to diversify; modern birds; expansion of grass lands Miocene 23.8 Tertiary Oligocene Elephants, horses; grasses 33.7 Mammals and flowering plants continue to diversify; first whales Eocene 54.8 Paleocene First primates; mammals, birds, and pollinating insects diversify 65 Widespread dinosaurs until extinction at end of Cretaceous; first flowering plants; present-day continents form Cretaceous Mesozoic era Phanerozoic eon Pliocene 144 First birds and mammals; cycads and ferns abundant; giant reptiles on land and in water Jurassic 206 Triassic 248 First dinosaurs; first mammals; therapsids and thecodonts; forests of conifers and cycads Fossil Record Evolution: Often the Record is Incomplete Only animals with hard body parts are fossilized Geological activity destroys many preserved specimens Fossils buried deep in the Earth or submerged in the depths of the oceans will likely never be discovered Figure 13.4 Fossil Record Evolution: Estimating the Age of Fossils Absolutedating Relative dating • Uses Placesradiometric fossils in adating sequence to assign of events an without age to a assigning fossil by testing a specific the age fossil itself • or Presumes the sediment that lower in which rockitstrata was found are • Radioactive older than higher isotopes layers decay at • characteristic Relative method and ofunchangeable determining rates • Half-life “oldest”=tothe “most timerecent” it takes for half the atoms in a radioactive sample to decay Living organism After death Organism incorporates 12C and 14C. 14C leaves as 14N. No new 12C or 14C added. 14C leaves as 14N. 14C 12C After death, proportion of carbon as 14C declines. Figure 13.5 Biogeography: The Theory of Plate Tectonics Today MYA Earth’s 280-200 181-135 100-65 surface MYA consists of several rigid layers, called tectonic plates • Where the plates collide, mountain ranges are formed • Where plates separate, new molten rock seeps to Earth’s surface Two All continents Present-day Continents major are continents joined into continue toform. form one drift supercontinent, and apart. begin to drift Pangaea. apart. North North America. America Europe Africa South South America America Asia Eurasia Laurasia India Africa India Australia Australia Antarctica Antarctica Figure 13.6 Biogeography: Species Distribution Fossil distribution indicates that the continents were once part of a super continent Africa India South America Australia Antarctica Biogeography: Species Distribution The rise and fall of marsupials • Diverse and abundant in South America until about 1 or 2 MYA • Invading placental mammals out competed the marsupials • Marsupials remain in Australia because its isolation kept them free of competition Figure 13.7 Biogeography: Species Distribution Wallace’s Line: • Alfred Russel Wallace noticed a unique assemblage of animals on either side of an imaginary line in the Malay Archipelago • “Wallace’s line” is a deep-water trench that separated the islands • The water barrier prevented migration between populations; evolution produced a unique variety of organisms on each side of the Wallace’s line Asia Philippines Africa Australia Malay Peninsula Borneo Sumatra New Guinea Sulawesi Java Wallace’s line Indian Ocean More like Asia Australia More like Australia Figure 13.8 Anatomical Comparisons: Homologous Structures Homologous structures have similarities that indicate common ancestry Homologous structures share a common ancestry, but may function differently Figure 13.9 Anatomical Comparisons: Vestigial Structures Vestigial structures have no apparent function in one organism, but appear to be homologous to a functional structure in another species Anatomical Comparisons: Convergent Evolution Convergent evolution – the evolution of similar adaptations in organisms that do not share the same evolutionary lineage, but encountered similar selection pressures Analogous structures – similar function but not in structure because of convergent evolution, not descent from a common ancestry (e.g. a bird’s wing vs. an insect’s wing) Figure 13.13 13.12 13.11 Embryonic Development Indicates Common Ancestry Homeotic The Vertebrate fetal skull genes embryos a expressed appear alike unequally in early Chimpanzee Human chimpanzee development result in different and , reflecting aanatomy similar development human have processes asthe cells divide and same parts, but differentiate follow different developmental pathways Area of gene expression Forelimb Homeotic gene A Homeotic gene B Forelimbs develop into wings Forelimbs absent Flank Flank Fish Mouse Hindlimb Hindlimb Chick Hindlimbs develop into legs Python Alligator Hindlimbs remain vestigial Figure 13.14 Molecular Evidence: Comparing DNA & Protein Sequences Cytochrome c Evolution DNA and protein similarities • It is highly unlikely that two unrelated species would evolve precisely the same DNA and protein sequences • It is more likely that the similarities were inherited from a common ancestor and the differences arose through mutation Organism Number of amino acid differences from humans Chimpanzee 0 Rhesus monkey 1 Rabbit 9 Cow 10 Pigeon 12 Bullfrog 20 Fruit fly 24 Wheat 37 Yeast 42 Figure 13.15 Molecular Evidence: Molecular Clocks Molecular clock • Uses a know mutation rate for a gene and the number of differences in the DNA sequences for that gene in two species • Estimates the time when the organisms diverged from a common ancestor ~ 50 million years later ~ 25 million years later G AC T T A G A C T G A C T T GG A C T Common ancestor DNA sequence Modern species 1 G A C T T G G A C T Common ancestor G A C T T A G G C T G A C T T AG G C T 50 MYA ~ 25 million years later ~ 50 million years later G A C C T AG G C T G A C C T A G G C C 25 MYA Today Modern species 2 G A C C T A G G C C Chapter 14 SPECIATION and EXTINCTION Species Names Carolus Linnaeus – assigned species a two-word biological name • Genus – a broader classification • Specific term For example, the human biological name is Homo sapiens • Genus – “Homo” • Specific term – “sapiens” Biological Species Concept A species is a population, or group of populations, whose members can interbreed and produce fertile offspring Does not apply to: • Asexually reproducing organisms • Extinct organisms • Organisms that would only interbreed in captivity • conditions when reproductive isolation is not absolute Speciation The formation of new species – occurs when some individuals can no longer successfully interbreed with the rest of the population • Reproductive isolation - the two groups could not produce fertile offspring • Macroevolution = large-scale evolutionary change Figure 14.3 Reproductive Isolation: Prezygotic Reproductive Barriers Habitat – different environments Prezygotic Reproductive Isolation Barrier Description Example Illustration Temporal – active or fertile at different times Habitat isolation Different environments Ladybug feed on different plants Temporal isolation Active or fertile at different times Field crickets mature at different rates Behavioral isolation Different courtship activities Frog mating calls differ Mechanical isolation Mating organs or pollinators incompatible Sage species use different pollinators Behavioral – different courtship rituals Mechanical – mating organs or pollinators incompatibility Sea urchin gametes are incompatible Gametic – gametes cannot unite Gametic isolation Gametes cannot unite Figure 14.3 Reproductive Isolation: Postzygotic Reproductive Barriers Hybrid inviability – hybrid offspring fail to reach maturity Postzygotic Reproductive Isolation Barrier Description Example Hybrid inviability Hybrid offspring fail to reach maturity Hybrid eucalyptus seeds and seedlings are not viable Hybrid infertility (sterility) Hybrid offspring unable to reproduce Lion-tiger cross (liger) is infertile Hybrid breakdown Second-generation hybrid offspring have reduced fitness Offspring of hybrid mosquitoes have abnormal genitalia Illustration Hybrid infertility (sterility) – hybrid offspring is unable to reproduce Hybrid breakdown – second-generation hybrid offspring have reduced fitness Figure 14.4 Spatial Patterns Define Two Types of Speciation Allopatric speciation • Geographic barrier separates a population into two groups that can no longer contact one another • Natural selection and genetic drift act independently on each group resulting in eventual reproductive isolation No contact between populations Figure 14.4 Spatial Patterns Define Two Types of Speciation Sympatric speciation • Reflects the fact that a habit that appears uniform actually consists of many microhabitats • Organisms may specialize to different zones resulting in eventual reproductive isolation Continuous contact between populations Figure 14.9 The Pace of Speciation Gradualism = one species transforming into another through a series of small, incremental changes over many generations Gradualism Punctuated equilibrium Punctuated equilibrium = long periods of little change interrupted by relatively brief bursts of rapid evolutionary change Time Extinction Extinction = the complete disappearance of a species • Background extinction rate = steady, gradual loss of species through natural competition or the loss of genetic diversity • Mass extinction = great numbers of species disappear over a relatively short expanse of time Precambrian Mesozoic Paleozoic Cenozoic Total extinction rate (families per million years) 20 15 10 5 0 600 400 Time (MYA) 200 0 Taxonomy & Taxonomic Hierarchy Taxonomy = the study of describing, naming, and classifying organisms • Systematics = the study of classification • Phylogenetics = the study of evolutionary relationships among species Carolus Linnaeus – organized life into a hierarchical classification system Linnaean Taxonomic Hierarchy Linnaean classification of the plant Aloe vera (in descending order): Taxonomic group Aloe vera plant found in: Number of species Domain Eukarya Several million Kingdom Plantae ~375,000 Anthophyta ~235,000 Class Liliopsida ~65,000 Order Liliales ~1200 Family Asphodelaceae 785 Genus Aloe 500 Species Aloe vera 1 Phylum Figure 14.14 Cladistics Cladogram– –the Phylogenetic Outgroup tree-like system basis that for diagram comparison defines thatgroups infer in by evolutionary cladistic an distinguishing analysis relationship to between determine ancestral whichand derived characters characters are ancestral and which are • Ancestral character = an inherited derived attribute that resembles that of the Clade ancestor = a group of organisms consisting • Derived of a common character ancestor = aand feature all ofnot its found descendants in the ancestor Clades Birds Non-avian dinosaurs Crocodiles Node (common ancestor) Lizards and snakes Turtles Last common ancestor Mammals Amphibians “Traditional” Groups Are Not Clades Traditional groups such as endotherms (“warm-blooded” animals) refers to a character of convenience and does not make reference to the common ancestor of all endothermic animals